Failure diagnosis apparatus of EGR system

Abstract

In the engine including an MPL-EGR system having an HPL-EGR mechanism 6 and an LPL-EGR mechanism 7 , a pressure difference between upstream side pressure and downstream side pressure of a low pressure EGR cooler 73 provided in the LPL-EGR mechanism 7 is detected by a pressure difference sensor 89 . When an actual pressure difference value detected is higher than a reference pressure difference value in a state where no blocking occurs in the LPL-EGR mechanism 7 , and the deviation amount therebetween reaches a predetermined amount, it is determined that the blocking occurs in the inside of the low pressure EGR cooler 73 . In contrast, when the actual pressure difference value detected is lower than the reference pressure difference value, and the deviation amount therebetween reaches a predetermined amount, it is determined that the blocking occurs in the inside of the pipe members 74 and 75 except the low pressure EGR cooler 73.

The invention claimed is: 
     
       1. A failure diagnosis apparatus of an EGR system comprising a pipe member and an EGR cooler linked to the pipe member and configured to recirculate part of exhaust gas discharged into an exhaust system of an internal combustion engine to an intake system via the pipe member and the EGR cooler, said failure diagnosis apparatus comprising:
 an electronic control unit configured to: 
 receive a pressure difference between upstream side pressure and downstream side pressure of the EGR cooler from a pressure difference sensor; 
 compare a pressure difference value detected by the pressure difference sensor with a predetermined cooler blocking determination value and a predetermined pipe blocking determination value that is smaller than the cooler blocking determination value; and 
 determine that, when the pressure difference value detected is greater than the cooler blocking determination value, blocking occurs in an inside of the EGR cooler, and determine that, when the pressure difference value detected is smaller than the pipe blocking determination value, blocking occurs in an inside of the pipe member, 
 wherein a location of the blocking is written to the electronic control unit. 
 
     
     
       2. The failure diagnosis apparatus of the EGR system according to  claim 1 , wherein the cooler blocking determination value is set as a value corresponding to a blocking degree of the EGR cooler with respect to a deterioration allowance limit of exhaust emission specified in advance. 
     
     
       3. The failure diagnosis apparatus of the EGR system according to  claim 1 , wherein the pipe blocking determination value is set as a value corresponding to a blocking degree of the pipe member with respect to a deterioration allowance limit of the exhaust emission specified in advance. 
     
     
       4. The failure diagnosis apparatus of the EGR system according to  claim 1 ,
 wherein the pipe member comprises an upstream side pipe member linked to an upstream side of the EGR cooler and a downstream side pipe member linked to a downstream side of the EGR cooler, 
 wherein 
 the pressure difference sensor detects the pressure difference by taking as the upstream side pressure a pressure at a linking portion between the EGR cooler and the upstream side pipe member or at a position nearer to the EGR cooler than to the linking portion and taking as the downstream side pressure a pressure at a linking portion between the EGR cooler and the downstream side pipe member or at a position nearer to the EGR cooler than to the linking portion. 
 
     
     
       5. The failure diagnosis apparatus of the EGR system according to  claim 1 ,
 wherein the EGR system comprises a high pressure EGR mechanism configured to recirculate exhaust gas on an upstream side of a turbine of a supercharger in the exhaust system of the internal combustion engine to the intake system, and a low pressure EGR mechanism configured to recirculate exhaust gas on a downstream side of the turbine of the supercharger in the exhaust system to the intake system and include the EGR cooler, and 
 wherein the pressure difference sensor is configured to detect a pressure difference between the upstream side pressure and the downstream side pressure of the EGR cooler in the low pressure EGR mechanism, so as to determine a blocking portion in the low pressure EGR mechanism. 
 
     
     
       6. The failure diagnosis apparatus of the EGR system according to  claim 1 ,
 wherein the electronic control unit is further configured to assume a recirculation amount of the exhaust based on parameters including the pressure difference between the upstream side pressure and the downstream side pressure of the EGR cooler detected by the pressure difference sensor, an opening degree of an EGR valve that adjusts the recirculation amount of the exhaust gas, an exhaust gas temperature, and exhaust gas pressure.